1. Field of the Invention
The present invention relates to a method of manufacturing an electromagnet including a stacked body, and the electromagnet.
2. Description of the Related Art
Conventionally, electromagnets of various structures which are used for voice coil motors and the like have been disclosed. JP 62-77048 A discloses a voice coil motor which includes an electromagnet formed by using a stacked body.
The electromagnet disclosed in JP 62-77048 A includes a plurality of layers of insulating base materials on which linear conductors having spiral shapes when seen from a plan view are formed. The linear conductors which are formed on adjacent insulating base materials in a stacking direction and have spiral shapes when seen from a plan view, spiral in opposite winding directions. Inner circumferential ends of a pair of linear conductors whose winding directions are opposite are connected by a conductor which penetrates the insulating base materials.
When thermoplastic resin is used for the insulating base materials to manufacture an electromagnet of such a structure, the following problem occurs. FIGS. 12A and 12B are sectional views illustrating the problem of a stacked electromagnet which uses insulating base materials made of thermoplastic resin. FIG. 12A illustrates a state before thermocompression bonding, and FIG. 12B illustrates a state after the thermocompression bonding.
First, as illustrated in FIG. 12A, wound linear conductors 301, 302 and 303 are formed on surfaces of a plurality of insulating base materials 201, 202 and 203. A plurality of insulating base materials 201, 202, 203 and 204 (201 to 204) is stacked sandwiching the linear conductors 301,302 and 303 between the linear base materials.
In this regard, the insulating base materials 201, 202 and 203 are stacked such that positions of the wound linear conductors 301, 302 and 303 overlap when seen from the stacking direction. Thus, the positions of the wound linear conductors 301, 302 and 303 are overlaid and the wound linear conductors 301, 302 and 303 are successively connected by a via conductor which is not illustrated to form one coil.
However, according to this configuration, when the insulating base materials 201 to 204 are thermocompression-bonded to form a stacked body 20P, the insulating base materials 201 to 204 are thermoplastic and therefore move.
In this regard, the number of layers (the number of layers of insulating base materials 30 the number of layers of linear conductors) which are stacked in a region in which the wound linear conductors 301, 302 and 303 are formed is larger than the number of layers (the number of layers of insulating base materials) which are stacked in a region 909 surrounded by the wound linear conductors 301, 302 and 303. Hence, when uniaxial pressing is performed upon thermocompression bonding, a pressure to be applied to a region in which the wound linear conductors 301, 302 and 303 are formed is larger than a pressure to be applied to the region 909. Further, the linear conductors 301, 302 and 303 do not melt at a temperature at which the insulating base materials melt.
Hence, the insulating base material between the linear conductors moves to another region, and thereby changes a positional relationship of each linear conductor in each layer. As illustrated in FIG. 12B in particular, at position at which the linear conductors are formed near the region 909, mobility of the insulating base material is great due to the difference in the number of layers. Hence, the linear conductors 301, 302 and 303 move, and the linear conductors 301, 302 and 303 formed in different layers unnecessarily approach each other and cause short-circuiting with the linear conductors in the different layers in some cases. Further, even when isotropic pressing is performed upon thermocompression bonding, significant movement and deformation occur in the region 909, and then the linear conductors move.